In the modern age, very few enterprises can work in vacuum, without interacting with other business management systems that are owned by their associates. You need reports to be submitted, forms to be filled, excel sheets to be exchanged with your colleagues within and without your own premises.
Tally has its own capabilities of data interchange; to export its own data in industry standard formats like HTML, EXCEL and XML. But there are two specific needs that a user faces:
Exporting the data as expected by the receiver
Importing the data from external sources
For both these requirements to be fulfilled, customization is required. Who else but APEX will provide you these services effectively?